The present invention relates to storage tanks and more particularly to a process for restoring the damaged bottom of a storage tank.
Storage tanks have many applications related to the production, refining and distribution of hydrocarbons. For example, storage tanks are a customary means for storing raw oil field products including crude oil or produced water at production sites. It has been found that the corrosive character of the raw products can damage the tanks in which the products are stored over time. Metallic tank bottoms are particularly susceptible to damage by corrosion or pitting from oil field liquids. Corrosion or pitting damage can ultimately breach the tank bottom, resulting in leakage of the stored liquids from the tank into the surrounding environment and harm thereto. Accordingly, it is imperative that such damage is rapidly and effectively repaired to restore the integrity of the tank, either as a preventive step prior to the occurrence of leakage from the tank or as remedial step after the occurrence of leakage to inhibit further leakage therefrom.
A number of corrective procedures applicable to storage tanks are known in the prior art. For example, the entire tank can be replaced in the case of severe and irreparable tank bottom damage. In less severe cases, tank repair options include replacing the damaged tank bottom with a new steel bottom, installing a steel or fiberglass patch over the damaged portion of the tank bottom, welding the damaged portion of the tank bottom, or overlaying a reinforced fiberglass liner atop the entire damaged tank bottom. Although each of these procedures may effectively restore the integrity of the tank bottom, none is entirely satisfactory because all require human entry into the tank and are relatively costly, time-consuming and labor intensive to perform, demanding a high degree of skill.
Another repair option is taught by U.S. Pat. No. 3,450,295, wherein a coat of foamed plastic material, such as a foamed resin, is placed over the damaged tank bottom. This procedure generally requires human entry into the tank, but is advantageously less costly and more rapid to perform than the procedures recited above. Nevertheless, this procedure requires a high degree of surface preparation for the tank bottom. In addition, placement of the foamed material requires a high degree of care in mixing the components of the foamed material and properly distributing the foamed material across the tank bottom. Finally, the load-bearing capacity of the foamed material is unduly limiting for many applications.
Yet another repair option is taught by U.S. Pat. No. 5,172,825, wherein a polymer gel plug is placed in the tank bottom to eliminate dead tank volume as well as to provide protection from leakage in the event of corrosion. This procedure generally does not require human entry into the tank and is relatively inexpensive and rapid to perform. Again, however, the load-bearing capacity of the polymer gel may be unduly limiting for many applications. As such a need exists for a more effective process of restoring the integrity of a damaged storage tank.
Accordingly, it is an object of the present invention to provide an effective process for restoring a damaged storage tank. More particularly, it is an object of the present invention to provide an effective process for restoring the bottom of a storage tank damaged by corrosion or pitting, wherein the tank has specific utility in hydrocarbon production, refining or distribution applications. It is another object of the present invention to provide a process for restoring the bottom of a storage tank that does not require human entry into the tank. It is another object of the present invention to provide a process for restoring the bottom of a storage tank that is cost effective. It is still another object of the present invention to provide a process for restoring the bottom of a storage tank that is relatively simple to perform. It is yet another object of the present invention to provide a process for restoring the bottom of a storage tank that requires relatively little time to perform. It is a further object of the present invention to provide a process for restoring the bottom of a storage tank that requires little or no surface preparation of the tank bottom. It is a still further object of the present invention to provide a process for restoring the bottom of a storage tank to a high load-bearing capacity. These objects and others are achieved in accordance with the invention described hereafter.
The present invention provides a process for restoring the damaged bottom of a storage tank. The process is initiated by preparing a slurry containing unconsolidated solids and a gelation solution. The unconsolidated solids are preferably in a particle form, such as conventional aggregates, or in a fiber form, such as conventional lost circulation materials used in drilling applications. The gelation solution includes an aqueous liquid solvent, a crosslinkable polymer, and a crosslinking agent. The crosslinkable polymer is preferably an acrylamide polymer and the crosslinking agent preferably includes a polyvalent metal cation selected from the group consisting of aluminum, chromium and mixtures thereof. The slurry is placed on the internal bottom surface of the storage tank in a sufficient amount to cover the surface. Preparation and placement of the slurry is effected either by dispensing the gelation solution and unconsolidated solids sequentially into the storage tank and forming the slurry in situ or by mixing the gelation solution and unconsolidated solids external to the storage tank to form the slurry and dispensing the premixed slurry into the storage tank.
After placement of the slurry on the internal bottom surface of the tank, the gelation solution is gelled substantially to completion in situ to form a gel that binds the unconsolidated solids, converting the slurry to a hardened continuous solid conglomeration containing the gel and solids. The hardened conglomeration provides a coat over the internal bottom surface of the storage tank having a relatively high load-bearing capacity that prevents further damage to the bottom of the tank and leakage therethrough.
The invention will be further understood from the accompanying drawings and description.